Retinoic acid (RA), the biologically active form of Vitamin A, is essential for a variety of biological processes. RA binds to nuclear receptors, retinoic acid receptor (RAR) and retinoid receptor X (RXR), to regulate target gene expression by triggering recruitment of coregulators that act, primarily, through chromatin remodeling and modification on the regulatory regions of target genes. Nuclear Receptor Interacting Protein 1 (NRIP1, originally known as RIP140) is a ligand-dependent co-repressor, i.e. it represses hormonal induction of target gene expression in a hormone-dependent manner. The long-term goal of this project is to understand the mechanisms underlying homeostatic control of vitamin A signaling. The proposal focuses on chromatin remodeling events orchestrated by RIP140 and coactivators that form complexes with hormone receptors, such as RIP140-RAR/RXR complex and coactivator-RAR/RXR complexes, as well as the biological significance of several newly identified post-translational modifications in the modulation of receptor/coregulator activities. Two questions will be addressed: 1) how does RIP140 function in hormone-induced chromatin remodeling? 2) How does protein modification regulate the biological activity of RIP140? Wild type and genetically modified cells, including RIP140-knockout (RIP-/-) and TRAP220-knockout (TRAP-/-) cells, as well siRNA mediated gene knockdown in P19 cells will be used as the principal experimental systems. Chromatin segments containing hormone response elements (HREs) will be the targets of examination to address mechanistic details in a physiologically relevant context. These studies will provide mechanistic insights into crosstalk of hormones (vitamin A and thyroid hormones) via coordinated formation of specific transcription factor complexes. These studies will also uncover potentially novel signals and cellular factors that are critical to cell differentiation program where vitamin A and other endocrine factors play vital roles. Knowledge gained from these studies could also be applied to understand clinical diseases that are affected by, or involve, hormonal and nutritional factors, such as metabolic diseases, the studies will also delineate the role of nutrients, such as vitamin A, in the maintenance of human health. PUBLIC HEALTH RELEVANCE: Retinoic acid (RA), the biologically active form of Vitamin A, is essential for a variety of biological processes. RA functions by regulating target gene expression through chromatin remodeling that involves Nuclear Receptor Interacting Protein 1 (NRIP1, originally known as RIP140). The long-term goal of this project is to understand the mechanisms underlying homeostatic control of vitamin A signaling. The current proposal focuses on the functional role of NRIP1 from a mechanistic stand point. Knowledge gained from these studies could also be applied to understand clinical diseases that are affected by, or involve, hormonal and nutritional factors, such as metabolic diseases. The studies will also delineate the role of nutrients, such as vitamin A, in the maintenance of human health.